Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities
Net income	$ 273	$ 107	$ 278	$ 342	$ (84)	$ 336	$ 270	$ 291	$ 1,000	$ 813	$ 899
Adjustments to reconcile net income to net cash flows provided by operating activities:
Net investment losses									(29)	52	(93)
Other, net									(225)	(223)	53
Net cash flows provided by operating activities									1,140	1,227	1,254
Cash Flows from Investing Activities
Change in short term investments									(535)	168	(6)
Other, net									15	18	20
Net cash flows used by investing activities									(225)	(177)	(424)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(929)	(896)	(842)
Proceeds from the issuance of debt									496	0	496
Repayment of debt									(520)	(180)	(391)
Purchase of treasury stock									(23)	0	0
Other, net									(12)	(9)	(18)
Net cash flows used by financing activities									(988)	(1,085)	(755)
Cash, beginning of year				310					310
Cash, end of year	242				310				242	310
Parent Company
Cash Flows from Operating Activities
Net income									1,000	813	899
Adjustments to reconcile net income to net cash flows provided by operating activities:
Equity in net income of subsidiaries									(1,119)	(930)	(1,032)
Dividends received from subsidiaries									1,065	1,026	955
Net investment losses									21	0	42
Other, net									13	16	36
Net cash flows provided by operating activities									980	925	900
Cash Flows from Investing Activities
Change in short term investments									10	130	(146)
Capital contributions to subsidiaries									(2)	(2)	0
Other, net									0	0	0
Net cash flows used by investing activities									8	128	(146)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(929)	(896)	(842)
Proceeds from the issuance of debt									496	0	496
Repayment of debt									(520)	(150)	(391)
Purchase of treasury stock									(23)	0	0
Other, net									(12)	(7)	(17)
Net cash flows used by financing activities									(988)	(1,053)	(754)
Net change in cash									0	0	0
Cash, beginning of year				$ 1				$ 1	1	1	1
Cash, end of year	$ 1				$ 1				$ 1	$ 1	$ 1